Lateral high-voltage transistors are commonly used in power management applications, such as power supplies for industrial and consumer electronic devices. A lateral high-voltage transistor used in such power management applications may be switched ON or OFF in response to control signals to convert a supply voltage into an output voltage which is suitable to power industrial and consumer electronic devices. In most high-voltage power management applications, of which the supply voltage may be as high as 1000V, it is desired that the lateral high-voltage transistor have a high breakdown voltage as well as a low on-resistance to ensure operation security and to improve the efficiency of power conversion.
Most existing lateral high-voltage transistors comprise a source region and a body region that are connected together to provide good ruggedness or safe-operating area (“SOA”) by suppressing the effect of a parasitic bipolar transistor, wherein the body region is connected to a substrate. Thus, the source region shares the same potential as the substrate. However, in some power management applications, a lateral high-voltage transistor having a source region that could assume a higher voltage than the substrate (typically connected to ground) is desired. Meanwhile, the lateral high-voltage transistor should still exhibit good capability of withstanding high-voltage without damage (i.e. should have a high-breakdown voltage) and good current carrying performance (i.e. should have a low on-resistance).
One way to allow the source region to assume higher voltage than the substrate is to separate the source region and the body region (do not connect them together), such that the body region is still connected to the substrate, but the source region can assume a voltage “floating” above the substrate voltage. However, in this case, the maximum source voltage is limited to the breakdown voltage between the source region and the body region, which is typically only about 10V. A further limitation of this approach is the degradation of the SOA because a base resistance of the parasitic bipolar transistor is increased due to increased distance from the source region to the body region.